A week ago, European parliamentary sources leaked the deal that British Prime Minister Theresa May was hoping to conclude with the European Union, and which would mean Northern Ireland remaining in “continued regulatory alignment” with the EU after Brexit. The obvious interpretation was that the UK was planning to cut Northern Ireland loose and effect a social, economic, and administrative merger of the whole island of Ireland. Ulster’s main Protestant grouping, the Democratic Unionist Party (DUP), duly screamed, and the proposed deal collapsed. After a week of further negotiations led by May, culminating in a early morning press conference on Friday in Brussels, the UK-EU deal was revived. But its present form is essentially a decision not to decide. No new regulatory barriers will exist between Northern Ireland and the rest of the United Kingdom unless and until the (Protestant/Unionist-dominated) Northern Ireland Executive and Assembly “agree that distinct arrangements are appropriate for Northern Ireland.” But that is never going to happen. A large Orange Protestant can has been vigorously kicked down the road.

The island of Ireland consists of both an independent republic of 26 counties, as well a six-county province—Northern Ireland, or Ulster—that is part of the United Kingdom. That division has through the years produced bitter conflicts, as the existence of the North remains offensive its Catholic minority who want a united Ireland. That both Great Britain and the Irish Republic were members of the European Union proved immensely beneficial at soothing tensions and effectively eliminating the internal border.

But what will happen when Great Britain leaves the EU while Ireland remains? There will have to be some frontier between northern and southern Ireland to check goods and/or migrants entering “Europe.” This can be done in two ways, each one desperately unpalatable to a major constituency. If there is to be a border, the obvious solution is to restore the long frontier across Ireland, with all its checkpoints and search controls, which the Republic finds utterly unacceptable (so also do most of Ulster’s Catholic minority).

Alternatively, Northern Ireland could be harmonized with the Republic and the rest of Europe, so that the de facto frontier would lie between the two islands, Britain and Ireland. Attractive as it sounds, it’s toxic for the province’s Protestant minority, as it would de facto unite the entire island under the control of Dublin and the Republic, and require some kind of border or checks between Northern Ireland and what we still notionally call “the rest of” the United Kingdom.

So there will and must be a border, either on land or in the Irish Sea, and choosing between the two is virtually impossible. Yet EU negotiators demanded that this quandary be resolved before Britain could even begin formal negotiations with Europe over its future trade relationship. (Those are also impossible but that’s a different story). Unlike other diplomatic issues, moreover, this particular nightmare had the potential to reignite actual violence and terrorism in Northern Ireland, a threat most people had believed solved after the Good Friday agreement of 1998.

One would think, then, that the British government would be hyper-cautious in proceeding in this area above all. Yet they’ve fallen far short of this standard, as was best demonstrated back in 2016 when the British Brexit minister David Davis referred to the border between Ulster and the Republic as an “internal” border, suggesting he did not know that the Republic is an independent state.

That is a bare narrative of events, one that admittedly ignores the real depth of the British policy disaster when it comes to Ireland and Brexit. Let’s examine the DUP, the Democratic Unionists, and pay particular attention to that latter word, which summarizes their whole raison d’être. They exist to preserve, protect, and defend the union of Northern Ireland and Great Britain, to which all other causes and beliefs are subsidiary. Yet Theresa May somehow hoped to slip Northern Ireland’s “continued regulatory alignment” with the EU past these Unionists as a fait accompli, without prior consultation, presumably on the assumption that they would happily go along with their near-severance from the UK.

But wait, there is more. From the 1920s, the dominant Protestant force in Northern Ireland was the Ulster Unionist Party (UU), which British observers used to think of as incomprehensibly extreme and implacable in its beliefs. Yet as the terror crisis grew worse in the 1970s, even the UU became too moderate, and support shifted to a much harder-line and more explicitly religious movement inspired by the Reverend Ian Paisley. That grouping became the DUP, which is not merely unionist, but extremely, extremely unwilling to accept anything smacking of compromise. Today, the DUP is by far the most powerful party in Ulster, holding 10 seats in the UK parliament.

That same DUP is also critical to the survival of Theresa May’s government. Last June, May suffered a disastrous election disappointment, when she lost her parliamentary majority and was forced to rely on those suddenly precious 10 DUP votes. By the way, May’s own party is called the Conservative and Unionist Party, and many of her pro-Brexit allies take that latter element very seriously.

What did May think was going to happen? Could anyone with the slightest knowledge of Northern Ireland have failed to tell her that what she was planning would be condemned as treason, and that it would assuredly provoke the DUP into moving towards resolute opposition, bringing down her government? Did nobody tell her what the “U” stood for?

Around the world, governments fall, careers are destroyed, but nobody actually gets hurt. This is not the case in Northern Ireland, where political disaster could yet raise some truly frightening ghosts. Most foreign observers are very familiar with Catholic/nationalist groups like the Irish Republican Army and its offshoots, but few know much about the deadly Protestant/unionist tradition associated with names like the Ulster Volunteer Force and the Red Hand Commando. From the 1960s through the 1990s, the UVF and other Protestant terror groups fought viciously against Catholics and nationalists, claiming some 600 lives—fewer than the IRA, but still a dreadful record of violence. Some of these actions were uniquely hideous even in the context of a terror war. One legendary group, nicknamed the Shankill Butchers, murdered dozens of Catholic civilians, torturing, mutilating, and in some cases killing their victims with hundreds of stab wounds.

Like the IRA, the Protestant terror groups largely disarmed or went underground after the 1998 peace settlement. As with the IRA, though, diehards remain, and they await only the opportunity to kill and maim once more for the cause of union. If a British government erected its EU border in the Irish Sea, the militants would very likely resurface. The DUP knows this particularly well, having itself benefited from its own hardline history. If the DUP compromised today, it senses acutely that other more extreme movements wait in the wings. And if the DUP replaced the UU, why could it not eventually be supplanted by the still more right-wing Popular Unionist Party or some equivalent successor?

That is the peril May and Davis were playing with—and seemingly without a clue as to the catastrophic dangers they faced. This is unforgivable.

On a whole different level of seriousness, David Davis has just revealed details of the planning that his government has undertaken about the likely economic impact of Brexit on various sectors of the British economy—automotive, aerospace, pharmaceuticals, and so on. He has now explicitly stated that because economic models are largely unreliable, no impact analysis statements have occurred, nor will they. Nothing, nada, none. Nor has he announced an intention to resign.

Theresa May’s latest visit to Brussels is being celebrated as a breakthrough—but it still doesn’t address the fundamental issues that have the potential to make Brexit a disaster for Britain. And with the specter of the Troubles looming again in Ireland, her government is guilty of gross negligence.

Philip Jenkins teaches at Baylor University. He is the author of Crucible of Faith: The Ancient Revolution That Made Our Modern Religious World.